1. Field of the Invention
The present invention relates to an expandable spinal implant apparatus and a method of using the apparatus to treat a spine disorder. More particularly, the present invention relates to an intervertebral spacer arranged for expansion of one or more dimensions of the spacer without canting, tilting, or slipping, and methods of using the expandable spacer.
2. Description of the Prior Art
Back pain can be caused by any one of several problems that affect the vertebral discs of the spine. These problems include, for example, degeneration, bulging, herniation, thinning of a disc, or abnormal movement, and the pain that is experienced generally is attributable to friction or pressure that inevitably occurs when one adjacent vertebra exerts uneven pressure, or when both adjacent vertebrae exert such pressure, on the disc. Back pain may also be attributed to neural element injury.
Whenever an individual suffers from a disc problem, a typical remedy is to perform interbody, intervertebral, cervical, thoracic or lumbar fusion (all generically referred to herein as IF) surgery on the patient for the purpose of fusing the two vertebrae that flank the defective disc to form a single, solid bone mass. Existing IF techniques generally involve removing the offending disc from the patient, adding bone graft material into the interbody space between the flanking vertebrae, and also inserting a spinal implant device into that space to hold the graft material in place and to support the flanking vertebrae while solid bone mass forms.
Existing IF techniques fail to enable fine positioning or stable expansion of an implant device with respect to the vertebrae. A brief discussion of the basic anatomy of the human spine, and specifically, the lumbar vertebrae of the spine, will help better illustrate this limitation. FIG. 1 shows a representation of a human vertebral disc 310, as it is arranged between a superior vertebra 320 and an inferior vertebra 330, in a partial representation of the lumbar region of a human spine. Specifically, the disc 310 is positioned between bottom surface 321 of the superior vertebra 320 and top surface 331 of the inferior vertebra 330. FIG. 2 shows a representation of the top surface 331 of the inferior vertebra 330. The inferior vertebra 330 includes a vertebral body 332 formed by a cortical rim 333, which is a dense, hard shell that is formed by compact bone, and an end plate portion 334, which is formed by much softer and less compact end plate material.
Referring to FIG. 3, existing IF procedures, including those associated with the lumbar region, involve positioning one or two spinal implant devices (an exemplary existing spinal implant device is shown as element 350 in FIG. 3) substantially centered on the end plate portion 334 of the inferior vertebra 330 and the bottom surface 321 of the end plate portion of the superior vertebra 320. Positioning the device in this way does not promote lordosis. Further, in this position, the device 350 tends to depress upon, or even become embedded in, the end plate portion 334 of the inferior vertebra 330 and/or the opposing end plate portion 324 of the superior vertebra 320. This settling of the implant device is referred to as subsidence. When this subsidence occurs, the vertebrae-supporting properties of the device 350 are reduced or eliminated. The result may be loss of intervertebral space height and/or less than desirable coronal and/or sagittal alignment of the spine.
Existing IF procedures are further limited in other ways. During IF surgery, the surgeon must navigate the spinal implant device through a region that is densely packed with neural elements, muscle, ligaments, tendons and bone to access the top surface 331 of the inferior vertebra 330. In existing IF techniques, this requires extensive cutting and/or manipulation of this region, which can extend patient recovery time and subject the patient to other side effects, such as, for example, inflammation, which can be discomforting. Worse, in some patients, the patient must be entered in two or three of three possible body areas (i.e., the patient's posterior region in a posterior interbody fusion technique, the patient's anterior region in an anterior interbody fusion technique, laterally in a lateral interbody fusion technique and/or the patient's transforaminal region in a transforaminal interbody fusion technique) for the purpose of positioning the spinal implant device. It is also to be noted that existing IF techniques are substantially invasive and can be difficult to perform.
One aspect of the limitation of the existing tools used in the IF process relates to the design of the spacer. In some IF procedures, locating the spacer in the position of interest cannot be done by hand alone. Instead, a tool is required to push the spacer to the position of interest, particularly when promoting lordosis is the goal. Present spacers are configured so that the interface with the positioning tool occurs only on the primary longitudinal axis, one of the orthogonal axes, of the spacer. For example, the spacers are rectangular and include a port that is centrally aligned with the primary longitudinal axis of the spacer used to releasably receive the positioning tool therein.
Some spacers include a mechanism for changing the dimensions of the spacer, such as the height dimension. The mechanism permits dimension change after the spacer has been placed at or near the location of interest. The ability to change the height dimension of the spacer improves the chance of achieving desired intervertebral space height as well as coronal and sagittal balance. The present mechanisms may not produce uniform expansion of the spacer. As a result, the spacer may get caught on itself along one side, in a corner, etc., and will end up with a non-uniform height. The spacer is less effective than desired in such a canted state. It can cause pain for the patient and extend the recovery period, possibly with less than complete fusion established.
Another problem with existing expansion mechanisms relates to spacer rocking. That is, for a two-piece spacer in which one part extends from a base piece, the tolerances between the two pieces may be significant enough that the extension piece will rock or pivot on the base piece when in an extended position. This, too, produces a spacer of non-uniform height. The spacer is less effective in producing the desired intervertebral space height and/or coronal/sagittal alignment.
What is needed therefore is an expandable spinal implant apparatus configured to ensure uniform expansion with minimal or no rocking, canting, tilting, or slipping during and after the expansion process. Such an apparatus would decrease patient risk, speed recovery and substantially improve success rates in terms of restoration of normal spinal confirmation (i.e., intervertebral space height as well as coronal and sagittal alignment) and neurological decompression.